---
title: sapply() Function
---
## sapply() Function

The `sapply()` function is part of a family of `apply()` functions that aide in manipulating data. It takes 2 or more parameters and it returns a vector or matrix. The first parameter could be a vector or a data frame. The second parameter is usually a function you want to use along the elemnts of columns of the first parameter. 

You can use sapply to get the max of every column in a data frame as a vector.

```r
df <- data.frame(a = c(49, 12, 32, 21, 16), b = c(22, 39, 8, 54, 26))
df
#      a    b   
# 1   49   22  
# 2   13   39   
# 3   32    8   
# 4   21   54  
# 5   16   26  
df <- sapply(df, max)
df
#  a   b
# 49  54  
```

In the above example, the data frame itself is transformed by using `sapply()` on it directly.

You can also use `sapply()` within a function.

```r
df <- data.frame(a = c(49, 12, 32, 21, 16), b = c(22, 39, 8, 54, 26))
df
#      a    b   
# 1   49   22  
# 2   13   39   
# 3   32    8   
# 4   21   54  
# 5   16   26  

# Function to get the max number of every column for any dataframe
colMax <- function(data) sapply(data, max)

# maxes is a vector with the max number of every column in data frame df
maxes <- colMax(df)
maxes
#  a   b
# 49  54
```

You can use various different built in R functions such as `sqrt`, `min`, or `mean` with `sapply()` function.

## Resources

- [Study Trails](http://www.studytrails.com/r/core/control_structures_r_apply_functions/)
- [bookdown](https://bookdown.org/rdpeng/rprogdatascience/loop-functions.html)
- [DataCamp](https://www.datacamp.com/community/tutorials/r-tutorial-apply-family)
- [Advanced R](http://adv-r.had.co.nz/Functionals.html)